1. Field of the Invention
The invention relates to a sound reproducing system comprising headphones with sound generating means and means for controlling the sound signal generated by said headphone sound generating means to simulate external sound sources.
The invention also relates to a headphone for a sound reproducing system.
2. Description of the Related Art
Headphones are used in and for audio equipment, such as (mobile) CD-players, but also in call-in centers.
The headphones comprise a means for generating sound (usually a small loudspeaker). A recorded sound signal (voice or music) is sent to the headphones) and sound generators inside the headphone generate a sound. The listener will, however, perceive the generated sound as being generated inside or very near the listener""s head (which in fact it is), unless the sound signal is adapted. Such a sound is perceived to be unnatural. It is known to process the signals such that the perception of the sound signal by the listener is such that he/she believes to hear external sound sources, i.e., the listener perceives a more natural sound. To achieve this, the signals are processed through a filter set to alter the characteristics of the signal such that the sound generated near, or within, the head simulates an (or more than one) external sound source(s). An important aspect in this respect is the transfer characteristics of sound by an external source to the head and the pinnae of the ear itself, the so-called Head Related Transfer Function (HRTF), i.e., the manner in which sound becomes attenuated and altered by the head and pinnea itself before it actually is heard. Attempts to process the signals taking into account the HRTF to obtain external source simulation, are known from J. Acoust. Soc. Am. 85(2), pages 858-878, F. L. Wightman and D. Kistler, February 1989: xe2x80x98Headphone simulation of free-field listening I and IIxe2x80x99.
Such attempts, however, do not always prove to be successful. The HRTF is dependent on the actual shape and form of the head and the ear and differs substantially from one person to another. Furthermore, head movements complicate matters as they also influence the sound perception.
Japanese patent application JP 08/079,900 A discloses providing the headphones with measuring devices to measure the distance between the ears, the height of the head and head movements. Although such measurements can be used to improve the sound reproduction, the results leave room for improvement. The HTRF is a strongly individual one which can only be approximately determined using the result of such measurement. Likewise the effect of head movements can only be approximately determined.
It is an object of the invention to provide a sound system as described in the opening paragraph with improved sound reproduction.
To this end, the system is characterized in that the headphones are provided with microphones, and the means for controlling comprises, or is coupled to means for regulating the sound production by the headphone sound generating means such that a signal registered by the microphones is substantially zero when at least one external sound source is operative in response to a signal, and means for recording the results of said regulating to influence external source simulating sound generation in the headphones and/or means for regulating the sound production by the headphone sound generating means, such that the difference between a signal registered by the microphones and a known signal is substantially zero, and means for recording the results of said regulation to influence external sound simulating sound generation in the headphones.
Each headphone is provided with a microphone. The microphone, which is located near or preferably in the ear, registers the sound generated by the headphone sound generating means as well as, in one aspect of the invention, by the at least one external source. The system comprises means for regulating the sound production by the headphone sound generating means such that the microphone registers a substantially zero signal when, simultaneously, at least one external source, in response to a signal, and the headphone sound generating means are active. The headphone then generates a, as far as the human perception is concerned, same auditive signal but of opposite sign as the external source(s). The system includes means for recording the results of the regulation. Thereafter, when the external source(s) (is) are shut off, or removed altogether, the sound perceived by the listener is the same as that for the external sources. The signal registered by the microphone will be equivalent to that when only the source would be operative. The relation between a signal sent to the source, such as a loudspeaker, and the signal sent to the headphone sound generating means to simulate such an external source, is then known. The data from the above-mentioned regulation are used for regulation of the sound signal to the headphones in such manner that the external source is simulated.
The relation between a signal sent to an external source; a signal sent to the headphone sound generating means and a microphone signal are thus measured. Such measurement does, however, not only give the relation between signals a (external source signal) and b (equivalent headphone signal), but also between signals b (headphone signal) and c (microphone signal) and signals a (external source signal) and c (microphone signal). These known relations can also, or separately, be used in another aspect of the invention as follows.
Once, for a xe2x80x98standard headxe2x80x99 or, in fact, for any head, the relations between signals a, b and c have been established, it is not, in all circumstances, i.e., for other heads, necessary to make further use of an external source with signal a. It suffices to know (and this is known) the microphone signal c corresponding to a particular external source signal a to regulate headphone signal b, if needed. When the headphone sound generating means xe2x80x98trulyxe2x80x99 (signal b) simulates an external source (signal a), a particular microphone signal (signal c) should be registered. This is the case on the xe2x80x98standard headxe2x80x99. However, when the headphone is put on another head, the HRTF will be different and the same signal b sent to the headphone sound generating means will generate a microphone signal cxe2x80x2 different from the particular microphone signal c because of the different HRTF. The system has means for regulating the signal b sent to the headphone sound generating means (to bxe2x80x2) in such manner that signal cxe2x80x2 is equal to signal c, for recording the regulation data, and for using the regulation data for further sound production to simulate external source(s).
It should be noted that while, in embodiments, the headphone sound generating means and the microphone will be often separate elements, in some embodiments, the headphone sound generating means (headphone loudspeakers) may double in function as the microphone, especially when such headphone sound generating means is placed inside the ear channel.
Preferably, the system also comprises means for storing the regulation data for a specific person.
This enables regulation data to be kept and coupled to a specific user. The next time this user uses the system, an incoming signal is filtered in the xe2x80x98rightxe2x80x99 or at least xe2x80x98nearly rightxe2x80x99 manner.
These and other objects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.